FIG. 1 illustrates an example environment for the performance of a method of placing a production or development well 210 into an earth formation F. In the illustrated example, the earth formation F comprises a first shale deposit or bed 230, a tight sand deposit or bed 231, and a second shale deposit or bed 232. The beds 230, 231 and 232 are located on top of a reservoir R. The reservoir R includes a first porous sandstone bed or reservoir compartment 233, and an intermediate shale bed 234 separating the first reservoir compartment 233 from a second sandstone bed or reservoir compartment 236. In this example, the first compartment 233 contains a first hydrocarbon, and the second compartment 236 contains a second hydrocarbon as well as water. The interface between the hydrocarbon and the water is indicated by an oil water contact (OWC) 235. The earth formation F also comprises a fault 240 across which the geological structures are not continuous. Beds 230′, 231′, 232′, 233′, 234′ and 236′ correspond to similar beds 230, 231, 232, 233, 234 and 236 across the fault 240. Similarly, an OWC 235′ corresponds to OWC 235.
In the method depicted in FIG. 1, a first pilot or exploration well 220 is initially drilled through the formation F. As the well 220 is being drilled, logging while drilling measurements indicative of the physical properties of the porous rock immediately surrounding the well 220 are acquired. These measurements may typically include natural gamma ray and resistivity measurements, as well as other types of measurements known by those skilled in the art. Additionally, or alternatively, the drill string used to drill the well 220 may be removed from the well 220 and a wireline-conveyed tool string may be introduced into the well 220 to acquire measurements indicative of the physical properties of the porous rock immediately surrounding the well 220. Typical operations performed by the wireline-conveyed tool string may include pressure measurements, formation fluid sample collections and sidewall core collections, as well as other types of measurements and/or collections known by those skilled in the art. The measurements collected while drilling and/or with a wireline tool string are interpreted and used to identify, for example, a location of the top of the reservoir 236, a type and/or economical value of the hydrocarbon contained in the beds 233 and 234, and a location of the OWC 235, among other things. Based on this and optionally other information, a drill string is introduced in the well 220 for a side-tracking well 210. The well 210 is typically a horizontal well located at a depth that maximizes the economical value of the expected production from the well 210. The well 210 may be steered geometrically along a predetermined trajectory using periodical measurement of the tilt of the bottom hole assembly, or geologically with respect to the boundary between the beds 232 and 233 using, for example, deep resistivity images of the formation encountered by the bottom hole assembly used to drill the well 210.
As shown in FIG. 1, as the well 210 is being drilled in bed 233, it may cross the fault 240. In some cases, such as when the fault 240 is permeable, the type and/or economical value of the formation fluid present in the bed 236′ is similar to the type and/or economical value of the hydrocarbon present in the bed 233. However, in other cases, the type and/or economical value of the formation fluid present in the bed 236′ is unknown and can not be inferred from measurements collected while drilling the pilot well 220. For example, the type and/or economical value of the formation fluid present in the bed 236′ may be significantly lower than in the bed 233. Thus, the depth or trajectory of the well 210, selected based on the knowledge of the reservoir fluid along the well 220, may not lead to a sufficient economical value of the well 210 past the fault 240. Further, even horizontal variations of the hydrocarbon in the bed 233 may exist. The compositional variations may require updating the trajectory 210 to increase its economical value.